Metal heating furnace



June 28, 1966 J- J. TIPPMANN 3,258,255

METAL HEATING FURNACE Filed July 51, 1963 l ll E JosEPl-fbfr/gm-flzmm. M, eli-mud ATTCRNEYS. l

United States Patent O 3,258,255 METAL HEATING FURNACE Joseph J. Tippmann, Peters Township, Washington County, Pa., assignor to Loftus Engineering Corporation, Pittsburgh, Pa., a corporation of Maryland Filed `luly 31, 1963, Ser. No. 298,844 4 Claims. (Cl. 266-5) The present invention relates to metal heating furnaces wherein heavy slabs of metal are brought to uniform temperatures for further processing. More particularly, the invention is concerned with means for removing from said metal slabs skid marks resulting from the initial heating operation.

As is well known in the art, heavy metal slabs from an initial ingot rolling operation are returned to a furnace for reheating prior to further reduction of the slabs to finished or semi-finished products. Conventionally, the slabs introduced into the entrance of the reheating furnace are disposed transversely of a plurality of transversely spaced water-cooled members referred to as skids, extending longitudinally of a portion of the length of the furnace. As successive slabs are introduced into the furnace, each entering slab pushes the previous slab or slabs along the said skids. These skids extend longitudinally on the initial heating chamber of the furnace exposing the slabs to hot combustion gases introduced above and below the skids, facilitating initial heating of the slabs upon al1 exposed surfaces thereof, except those surface portions in contact with the water-cooled skids.

The slabs, accumulating -upon the skids, subsequently pass olf the skids onto the refractory lined bottom of a heated soaking chamber wherein the slabs are intended to reach uniform temperature throughout before passing out of the furnace to the mills for further processing. This system works well, except that those slab surface portions having prior contact with said water-cooled skids do not always reach the desired uniform temperatures of the remainder of the slab while in the soaking chamber.

Such slab surface portions are referred to as skid marks and are apparent as undesired surface imperfections on the rolled product.

Prior art provisions for reducing or eliminating such skid marks, were to provide a plurality of longitudinally extending tunnels within the soaking chamber and beneath the slab skid marks. Through these tunnels were passed hot combustion gases intended to heat those slab surface portions directly over the tunnels and thus eliminate the skid marks. Sometimes these tunnels were provided with open tops exposing the metal to the direct action of the tunnel combustion gases. This was not satisfactory since the slab heating operation produces surface scale on the slab which was carried into the tunnel and soon filled same. Scale removal could not be accomplished without closing down the furnace and letting it cool down to substantially atmospheric temperature to permit workmen to enter and remove the scale. Sometimes these tunnels were provided with refractory covers closing the tops f the tunnels, but the heavy metal slabs would break or soon wear away the covers, permitting the tunnels to fill with scale.

In the present invention I proposed to use said heating tunnels within the soaking chamber hearth, beneath the skid marks upon the slabs within said chamber and to close the top of the tunnels with a suitable refractory. However, instead of disposing the top surface of the refractory covers in the plane of the floor of the soaking hearth, I have disposed the top surface of the covers slightly below the plane of the floor of the said hearth.

Admittedly, such construction will provide shallow recesses extending longitudinally of the soaking hearth above said tunnels. However, the slab portions moving over said shallow recesses will tend to sweep the scale therefrom, causing it to pass out of the recesses over the slab discharge end of the hearth.

Another and more important object of the invention is to initially protect the tunnel covers from contact with the slabs, thereby preventing breakage or wear thereof until the entire upper surface of the hearth wears down to the horizontal plane of the upper surface of the covers.

A further object of the invention is to form said tunnel covers of a type of refractory which when heated tends to glaze the exposed surfaces thereof and in effect act as a lubricant for the slabs moving thereover after the hearth surface has worn to the plane of the upper surface of the tunnel covers.

Other objects of the invention will be made apparent from the following description and the drawing forming a part thereof, wherein:

FIG. 1 shows a longitudinal section through the furnace illustrating a portion of the slab heating section and the adjacent soaking hearth;

FIG. 2 shows a transverse section taken on lines lI-II through the soaking hearth illustrating the relation between the slabs, the hearth slab supporting surface and the covering means for the heating tunnels.

Referring now to the drawing wherein is shown a heating furnace 1 through which a plurality of metal slabs 2 are pushed. The furnace may be of any suitable design comprising one or more conventional heating zones 3 extending to the charging end of the furnace. Extending longitudinally of zone or zones 3 are a plurality of transversely spaced water-cooled skid members 4 receiving vertical transverse support from members 5 and upon which the slabs 2 are received and intermittently advanced by a pusher (not shown). Beneath the skids 4 is a chamber 3a supplied with heated combustion gases from a plurality of suitable burners 6 spaced transversely of the chamber. Above the skids 4 the chamber 3 is heated by combustion gases from a plurality of suitable burners 7 spaced transversely of the chamber. The combustion gases ow from burners 6 and 7 towards the charging end of the furnace and are discharged to the atmosphere through a suitable stack (not shown). Beneath the skids 4 and between supports 5 are preferably a plurality of suitable clean out openings 8 for removal of scale falling from the heated moving slabs. The heating chambers 3 are provided with a suitable roof 9, side walls 10 and throat wall 11 in which are mounted the burners 7. Extending rearwardly from zones 3 and throat wall 11 is a soaking chamber 12 provided with a suitable roof 13, side walls 14 and end wall 15. Chambe-r 12 is provided with a refractory bottom wall or hearth 16 disposed in substantially the horizontal plane of the skids 4 and extending rearwardly therefrom but terminating short of the chamber end wall 15. Hearth 16 terminates in watercooled discharge skids 17 over which heated or soaked slabs 2 are discharged from the furnace through a suitable pivotally mounted door 18 for further processing.

'Extending longitudinally of the furnace and hearth 16 and spaced transversely thereof are a plurality of heating tunnels 19, as best shown in FIG. 2. Hearth 16 is cornprised of suitable refractory materials of substantial thickness. The tunnels 19 therein are shown as six in number and are aligned with the same number of watercooled skids 4 of the heating zone 3. Tunnels 19 would normally open through the upper face of hearth 16. Each tunnel 19 is transversely enlarged adjacent the surface of hearth 16, as at 23, and closed by suitable refractory blocks 20 supported therein. The upper faces of the blocks 20 are disposed below the horizontal plane of the outer face of hearth 16, providing a shallow depression D, in the hearth, beneath the skid marks on the lower surface of each slab moving over the hearth 16.

Combustion gas from burners 21 flow through each channel 19, beneath the slabs 2, towards the charging end of the furnace, mingling with such gases from burners 6. The hearth of the soaking chamber 12 is heated by combustion gases from burners 22 discharged into the chamber and flowing towards the charging end of the furnace.

In this manner the blocks 2 above each tunnel 19 are heated through their upper and lower faces and impart their heat upon the water-cooled skid marks of the slabs moving thereover. As shown in FIGS. 1 and 2 there are six tunnels 19 aligned with the six skid rails 4 adjacent the discharge end of the furnace and a pair of slabs 2 move through the furnace. Each slab 2 being supported by three transversely spaced skids 4. Alternately the slabs may be of a length to span all six skids. As a new slab is entered into the charging end of the furnace, the pusher (not shown) advances the entire line of slabs over the skids 4 and the soaking hearth 16. As shown in FIG. 1, suitable clean-out doors C may be provided in one or both side walls 14 of the hearth to remove undesirable accumulations of scale under some conditions resulting from construction or operation of the soaking chamber.

As stated, the hearth 16 and cover blocks 20 may be of any suitable refractory. Preferably such refractory would be of the type comprised of alumina and aluminum silicate with a minor amount of intercrystalline siliceous glass saturated with alumina. Such refractory materials are preferably melted and poured into molds to provide cast blocks of desired sizes. Such cast blocks of the said materials provide a long wearing surface subject to a minimum of expansion when heated. Additionally, a slight reaction between the iron oxide, in the form of scale from the heated slabs, and the blocks which facilitate removal of the accumulating scale by the moving slabs. Blocks -of such materials exhibit a glazed surface when heated in the hearth, which surface facilitates movement of the slabs thereover. Such refractory is commercially available.

The foregoing soaking hearth construction, independently of the refractory used, provides advantages over the prior art. The tunnels 19 Aare free from accumulation of scale from the slabs 2 and thus a uniform flow of combustion gases through the tunnels from burners 21 towards the charging end of the furnace is maintained. The temperature of such combustion gases is controlled through the use of known controls for the burners 21 of each tunnel.

Another advantage resides in substantial control of the deposit of scale upon the upper faces of blocks forming the roof of tunnels 19. This results from the tendency of the slabs 2, supported upon the elevated surfaces of hearth oor 16, to sweep scale accumulations from within the slight depression above blocks 20 towards the end ofthe hearth and over the discharge skids 17.

Additionally, as the surface of hearth 16 Wears from passage thereover of slabs 2, the depth of such depressions over blocks 20 decreases, with consequent better removal of scale from the surface of the block.

Much of the furnace structure disclosed in the drawing has not been specifically described or reference characters applied thereto. The omission of such details results from the fact that they are -conventional or subject to many variations which is no way affect the invention claimed herein. Such details as affect the invention are specifically identified and are applicable t0 the soaking chamber hearth of reheating furnaces. By way of example and not limitation, the tunnel covering blocks 20 are shown as recessed about 11/2 inches below the upper surface of hearth 16. Obviously this dimension may vary as desired, except that the depression is of a depth which preferably provides for the slabs sweeping the scale therefrom for better transfer of heat from the blocks 20 to the colder skid marks on the surfaces of the slab overlying the hearth 16 and blocks 20.

It will be understood that various changes may be made in the details of construction of the illustrated embodiment, without departing from the spirit of the invention or scope of the appended claims.

I claim:

1. In a metal slab reheating furnace having a heating section provided with water-cooled skids supporting the slabs moving therethrough and a soaking section provided with a refractory hearth over which the slabs move after leaving the said skids, the combination of,

(a) a plurality of channel shaped longitudinally extending recesses in the surface of said hearth aligned with .the said water-cooled skids,

(b) each said recesses having a refractory covering means supported therein with the bottom face of the covering means spaced above the bottom of the recess providing a tunnel for passage of combustion gases and (c) the .top surfaces of the said covering means being disposed below the adjacent slab supporting surfaces of the hearth providing a shallow depression protecting the covering means from contact with the slabs frnoving thereover until the adjacent hearth surfaces erode to the plane of said covering means.

2. The reheating furnace as defined in claim 1, wherein the spacing between the planes of the covering means top surface and .that of the hearth top surface is such that scale from the billets collecting upon the surface of the covering means is normally swept therefrom by movement -of the billet thereover.

3. The reheating furnace as defined in claim 1, wherein the refractory hearth is comprised of cast slabs of a melted mixture of alumina and aluminum silicate having a minor amount of intercrystalline siliceous glass saturated with alumina providing when heated a glazed surface over which the metal slabs freely move.

4. The refractory furnace as defined in claim 3, wherein ythe refractory covering means of each said recesses is of the same material forming said hearth.

No references cited.

WHITMORE A. WILTZ, Primary Examiner.

M. L. FAIGUS, Assistant Examiner. 

1. IN A METAL SLAB REHEATING FURNACE HAVING A HEATING SECTION PROVIDED WITH WATER-COOLED SKIDS SUPPORTING THE SLABS MOVING THERETHROUGH AND A SOAKING SECTION PROVIDED WITH A REFRACTORY HEARTH OVER WHICH THE SLABS MOVE AFTER LEAVING THE SAID SKIDS, THE COMBINATION OF, (A) A PLURALITY OF CHANNEL SHAPED LONGITUDINALLY EXTENDING RECESSES IN THE SURFACE OF SAID HEARTH ALIGNED WITH THE SAID WATER-COOLED SKIDS, (B) EACH SAID RECESSES HAVING A REFRACTORY COVERING MEANS SUPPORTED THEREIN WITH THE BOTTOM FACE OF THE COVERING MEANS SPACED ABOVE THE BOTTOM OF THE RECESS PROVIDING A TUNNEL FOR PASSAGE OF COMBUSTION GASES AND 